For men over the age of 14, a monthly self-exam of the testicles is an effective way of becoming familiar with this area of the body which enables the detection of testicular cancer at an early -- and very curable -- stage.
Why do you need to do it monthly?
Because the point of the self exam is not to find something wrong today. The point is to learn what everything feels like when things are normal, and to check back every month to make sure that nothing has changed. If something HAS changed, you will know it and you can do something about it.